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ADL5519

Data Sheet

Rev. C | Page 20 of 39

USING THE ADL5519

BASIC CONNECTIONS

The ADL5519 is specified for operation up to 10 GHz. As a result,

low impedance supply pins with adequate isolation between

functions are essential. A power supply voltage between 3.3 V

and 5.5 V should be applied to VPSA, VPSB, and VPSR. Power

supply decoupling capacitors of 100 pF and 0.1 μF should be

connected close to these power supply pins (see Figure 53).

The paddle of the LFCSP package is internally connected to

COMR. For optimum thermal and electrical performance, the

paddle should be soldered to a low impedance ground plane.

INPUT SIGNAL COUPLING

The ADL5519 inputs are differential but were characterized

and are generally used single ended. When using the ADL5519

in single-ended mode, the INHA, INHB pins must be ac-coupled,

and INLA, INLB must be ac-coupled to ground. Suggested

coupling capacitors are 47 nF, ceramic 0402-style capacitors for

input frequencies of 1 MHz to 10 GHz. The coupling capacitors

should be mounted close to the INHA, INHB and INLA, INLB

pins. The coupling capacitor values can be increased to lower

the input stage high-pass cutoff frequency.

The high-pass corner is set by the input coupling capacitors and

the internal 10 pF high-pass capacitor. The dc voltage on INHA,

INHB and INLA, INLB is approximately one diode voltage

drop below the supply voltage.

VPSA

5pF

18.7kΩ

2kΩ

FIRST

GAIN

STAGE

OFFSET

COMP

INHA

INLA

A = 9dB

CURRENT

STAGE

Figure 52. Single-Channel Input Interface

Although the input can be reactively matched, in general this

reactive matching is not necessary. An external 52.3 Ω shunt

resistor (connected on the signal side of the input coupling capaci-

tors, as shown in Figure 53) combines with the relatively high

input impedance to give an adequate broadband match of 50 Ω.

The coupling time constant, 50 × CC/2, forms a high-pass corner

with a 3 dB attenuation at fHP = 1/(2π × 50 × CC ), where C1 =

C2 = C3 = C4 = CC. Using the typical value of 47 nF, this high-

pass corner is ~68 kHz. In high frequency applications, fHP should

be as large as possible to minimize the coupling of unwanted low

frequency signals. In low frequency applications, a simple RC

network forming a low-pass filter should be added at the input

for similar reasons. This low-pass filter should generally be placed

at the generator side of the coupling capacitors, thereby lowering

the required capacitance value for a given high-pass corner

frequency.

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